A cell phone apparently left behind in a shopping cart at a Florida Wal-Mart has led to the arrest of a couple accused of recording themselves sexually abusing a 4-year-old girl.

According to the Lee County Sheriff’s Office, the citizen who found the phone at a Cape Coral Wal-Mart turned it over to authorities. They obtained a search warrant, accessed the device and allegedly discovered “numerous images that were sexual in nature and constituted child pornography.”

The phone also contained contact information for a detective assigned to the sheriff’s office sexual predator unit. That detective recognized the number on the phone as that of 33-year-old registered sex offender Alan Robert Johnson, according to a sheriff’s office press release.

Investigators executed a search warrant at Johnson’s North Fort Myers home and allegedly discovered evidence that he and 37-year-old Jennifer Sparks were producing child pornography using a cell phone camera. The press release stated that images and videos found on the phones and in the home “show Johnson and Sparks engaging in sex acts with a four-year-old female child.”

The girl, whose connection to the couple is not yet known, was not found in the home. She was later recovered by the Polk County Sheriff’s Office and is now in the custody of the Florida Department of Children and Families. DCF spokesperson Terri Durdaller told HLN that authorities are still investigating the case and are not sure how she ended up in the care of Johnson and Sparks.

The two suspects are being held without bond on charges of sexual assault of a child, directing or promoting sexual performance by a child and possession of obscene material. Public defender Kathy Smith, whose office currently represents both defendants, said Monday that she does not comment on pending cases.

Johnson pleaded guilty to federal child pornography charges in 2003, according to court records. He was sentenced to 70 months in prison and Federal Bureau of Prisons records show he was released in 2008.

According to 2003 reports in the Fort Myers News-Press, Johnson was accused in that case of spending several hours a night online viewing and downloading images of children engaged in sex acts with adults. He reportedly told the judge at his sentencing, “I hope to get help for my problem and put this behind me.